Does leaving doors open at stores waste good energy?

After a long discussion, Banff decided not to tell merchants they have to close their doors during cold weather, even if they do not have air cushions. Photo courtesy of Chad Townsend

Is open-door policy of stores during winter a wanton waste of fossil fuels?

Air cushions seem to work in at least high-traffic areas

by Allen Best

Grocery stories have been doing it for decades, but it’s still jarring to see open doors in shops during the middle of frigid winter.

It’s a device to tell customers, “Hey, we’re open.”

Does it also waste energy?

Both Banff and Aspen, places that both pride themselves on their environmental credentials, have decided that open doors aren’t a problem, even when it’s very cold outside.

In Banff’s case, the municipality has received scattered complaints that the open doors are not befitting a town that is premised on environmental excellence, within a United Nations heritage site.

Councilors agreed that it would be better to close the doors, but didn’t want to impede retail sales, according to the Rocky Mountain Outlook. No policy was adopted to force businesses to close their doors when it gets cold.

“I have heard from a lot of people concerned about the inappropriateness of what they see on Banff Avenue on a winter day, but I also know from family in retail, it really does make a difference whether people walk in the door,” said Leslie Taylor, a councilor.

“If the door is open, they do walk in. If it’s closed, they don’t. It’s a weird piece of human psychology, but I believe it to be true.”

Merchants also protested that many of them have invested in electric devices called air curtains, electric fans installed above the doors that effectively create a barrier.

In Aspen, a city council member asked Jeff Rice, the city’s utility efficiency manager, to study the open doors of businesses. After all, this is the municipality that adopted the Canary Initiative, the manifesto to dramatically reduce greenhouse gas emissions.

Rice checked all the doors on a cold day within six blocks of downtown Aspen, finding 24 of them open. Behind those 24 open doors, some businesses had no heat on. This was particularly true of the galleries. Managers of the galleries told him that customers will, if they have to take off their jackets, leave. So it’s better to be on the cold side, counterintuitive as that seems.

About one-third of the open doors also had air curtains. Although he had no experience with them, Rice used his infrared heat detectors. There was, he concluded, a great difference between the two sides of blowing air. In other words, the barriers do succeed in creating an invisible wall, keeping the chill out and the warmth in.

“There really wasn’t anything to pursue once I had checked it all out,” he told MTN.

Such air curtains are not new. An article in Howstuffworks.com explains that the first air curtain was patented in 1904. Since first showing up in grocery stores in the 1980s, they have become ubiquitous. Logic would suggest that big retailers have studied the numbers and decided that they are more effective than vestibules or other devices.

Surprisingly, just one study seems to have been done to measure the energy efficiency of air curtains as opposed to conventional doors or vestibules. That study was commissioned in 2012 by Air Movement and Control Association, a trade group, and conducted by Liangzhu (Leon) Wang, Ph.D., from the Department of Building, Civil and Environmental Engineering at Concordia University, in Canada.

Using a variety of energy modeling programs, he found that while air cushions required electricity, on balance they had a net energy benefit in preventing loss of heat from a building when compared with both single-entry doors or vestibules. He modeled this on climate zones from Miami, Fla., to Fairbanks, Alaska.

The effectiveness was more marginal in cooling-dominated climates such as Florida and Texas than in heat-dominated climates like Minnesota.

But Wang also noted that it matters which direction the door faces, especially as it relates to wind.

Again, this is just one study—and it’s probably healthy to wonder about a study commissioned by an industry group.

Two energy advocacy groups, Architecture 2030 and the U.S. Green Building Council, who were contacted for this article, said they had done no investigations of their own.

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About Allen Best

Allen Best is a Colorado-based journalist. He publishes a subscription-based e-zine called Mountain Town News, portions of which are published on the website of the same name, and also writes for a variety of newspapers and magazines.

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